1. Field of the Invention
The present invention relates to a magneto-resistance effect head which takes advantage of a magnetic multi-layer film showing a giant magneto-resistance effect.
2. Description of the Related Art
In a magnetic recording device such as a HDD, in order to improve recording density, such a trend as that a recording track width of a medium is decreased is prevailing. To compensate decrease of read output which accompanies the decrease of the recording track width, a highly sensitive magneto-resistance effect (MR) head is being required.
In particular, a MR head using a spin-valve film which shows a giant magneto-resistance effect is considered promising. A spin-valve film possesses a magnetic multi-layer film formed on a substrate by sequentially laminating thereon a ferromagnetic layer whose magnetization rotates corresponding to signal magnetic field (hereinafter referred to as free layer), a non-magnetic layer, a ferromagnetic layer which magnetization is pinned (hereinafter referred to as magnetic pinned layer), and an anti-ferromagnetic layer for pinning magnetization of the magnetic pinned layer.
In an MR head taking advantage of a spin-valve film, there are such problems in putting to practical use as Barkhausen noise which occurs due to discontinuous movement of Bloch wall of the free layer and read fringe in the neighborhood of both edge portions of a width direction of a read track. In order to solve such problems, for example, as shown in FIG. 22, an MR head of an abutted junction structure is proposed in which outsides of the both edge portions which deviate from recording track width W.sub.t of a spin-valve film 1 are etched to be eliminated and thereon hard magnetic layers 2 are respectively disposed as hard magnetic biasing films.
In a spin valve type MR head shown in FIG. 22, a spin-valve film 1 comprises a free layer 3, a non-magnetic layer 4, a pinned layer 5 and an anti-ferromagnetic layer 6. On the hard magnetic layer 2, to supply sense current to the spin-valve film 1 therethrough, electrodes 7 are formed respectively. Though not shown in the figure, the spin-valve film 1 is interposed between a pair of an upper and a lower magnetic shield layers disposed respectively through magnetic gap.
In an MR head of an abutted junction structure shown in FIG. 22, by vanishing magnetic domain of the free layer 4 with the bias magnetic field from the hard magnetic layer 2, Barkhausen noise is suppressed. Further, while leaving the spin-valve film corresponding to the read track width W.sub.t. the portions outside their edge portions are replaced by the hard magnetic layers 2. Therewith, recording information only from a recording track can be read, thereby read fringe can be made small.
Now, in order to respond to a further high densification of magnetic recording density, even in the spin valve type MR head, there is a demand in further narrowing the gap (thinning of the gap film). When the abutted junction structure is employed in an MR head having a more narrow gap, even if bias force is tried to be enhanced, for example, by making thick the thickness of the hard magnetic layer 2 serving as a hard magnetic biasing film, since the bias magnetic field leaks to the magnetic shield layer, it is difficult to obtain effective bias force.
As described above, in the spin valve type MR head, although the abutted junction structure is effective fundamentally in suppressing Barkhausen noise due to Bloch wall of the free layer, due to gap narrowing and track narrowing of the MR head, effective inputting of the bias magnetic field to the free layer is becoming difficult. In particular, when a track is made narrow, although the bias magnetic field should be effectively inputted, conversely, it has become clear that, as the track width becomes more narrow, Barkhausen noise becomes likely to occur. These facts are made clear for the first time through the results obtained by the present inventors.
From the above, in a spin valve type MR head of the abutted junction structure, it is required to clarify the causes of Barkhausen noise when the track width is made more narrow and to devise a countermeasure.